Uma Cs/Ps Split Architecture and Interface

ABSTRACT

An UMA network controller (SGW,D 1 ,D 2 ) is dedicated for an UMA mobile network comprising a CS core network (CN 2 ) with an MSC and a MGW, a PS core network (CN 1 ) with a SGSN. This UMA network controller comprises a) a security gateway (SGW), a PS part (D 1 ) and a CS part (D 2 ). The security gateway (SGW) is coupled to the MGW, to at least one PS part (D 1 ) and to at least one CS part (D 2 ), and arranged to ensure security procedures between mobile stations (MS) and the UMA world, and to forward messages relative to the control plan for both CS (CN 2 ) and PS (CN 1 ) core networks, and messages relative to the user plan for both the CS (CN 2 ) and PS (CN 1 ) core networks. The PS part (D 1 ) is intercalated between the SGSN(s) and the SGW, and arranged for forwarding user data between the SGSN and mobile stations (MS) through the SGW, and for handling the control plan for the PS core network (CN 1 ) through packet switched call messages over TCP. The CS part (D 2 ) is intercalated between the SGW and the MSC and arranged for handling the control plan for the CS core network (CN 2 ) and discovery and registration procedures of the mobile stations (MS), for forwarding packet switched call messages over TCP between a PS part (D 1 ) and the mobile stations (MS) through the SGW, and for relaying circuit switched call messages between the MSC and the mobile stations (MS) through the SGW.

The present invention relates to the domain of mobile (or cellular)communication networks, and more precisely to mobile communicationnetworks of the UMA (Unlicensed Mobile Access) type, defined by thetechnical specifications of the 3GPP TS 43.318 v6.4.0, “Generic accessto the A/Gb interface—stage 2” (release 6), and TS 44.318v6.3.0—“Generic Access (GA) to the A/Gb interface, Mobile GA interfacelayer 3 specification” (Release 6).

As it is known by the man skilled in the art, an UMA network mustcomprises UMA access node called UNC (UMA Network Controller) tointerface with mobile switching center(s) (MSC) belonging to its circuitswitched (CS) core network and to serving GPRS support node(s) (SGSN)belonging to its packet switched (PS) core network.

In order a mobile station could exchange data with the UMA network, apermanent TCP (Transmission Control Protocol) connection must beestablished with an UNC, through which the CS and PS protocols aresupported, after an authorization phase. Since a TCP connection isnatively a transport connection oriented protocol, an UNC is astandalone machine supporting altogether CS and PS services, accordingto the 3GPP UMA standard.

From a network topology perspective, an UNC is comparable to a GERAN BSC(GSM EDGE Radio Access Network Base Station Controller) as it offersaccess to a core network by means of A and Gb interfaces respectivelyfor CS and PS core network parts.

A BSC of a GERAN necessitates solid CPU capacities to handle radioresource management algorithms and plays a role of concentration node ina TDM transmission network organized with base stations (BTSs) in a starconfiguration. Therefore altogether for CPU reasons and transmissionnetwork organization, the BSCs are very justified as dedicated accessnetwork nodes.

An UMA access network having a number of specificities compared to aGERAN network, an UNC i) must have much less CPU requirements as it doesnot handle radio resource management algorithms with complex radiooptimization features, ii) is merely a protocol gateway function for theCS core network part and a forwarding machine for the PS core networkpart, and iii) supports WiFi access point through a native IP networkand therefore is not subject to any topology constraints linked to TDMtransmission network.

So, even though an UNC stands as a BSC in a GERAN model, it has littleto do with a radio communication equipment and is more a core networktype node as it is a kind of access server combined with a protocolrelay and a traffic forwarder.

Moreover, no manufacturer offers a combined MSC/SGSN product.

So, the object of this invention is to improve the situation bysplitting an UNC into UNC-CS and UNC-PS parts linked through a specificinterface, having features such as i) supporting the UNC splitting whichhas not been provide for by the 3GPP UMA standard, ii) allowing anefficient communication between UNC-CS and UNC-PS parts, iii) supportinga high availability operation, iv) overcoming a number of difficultieslinked to particular UMA network topology constraints (e.g. whenoperating with a limited number of UMA cells), v) supporting loadsharing, vi) supporting optimized operator radio resource usage, vii)providing a set of additional control features allowing the UNC-CS partto have control on the GPRS resource usage, and more precisely push toUNC-PS part of resource description and allocation policy (e.g.globally, per routing area (RA)).

For this purpose, it provides an UMA network controller (UNC) for an UMAmobile communication network comprising a circuit switched core networkwith at least one mobile switching center (MSC) and a media gateway(MGW), a packet switched core network with at least one serving GPRSserving node (SGSN).

This UMA network controller (UNC) is characterized in that it comprisesa security gateway (SGW), a packet switched part (UNC-PS) and a circuitswitched part (UNC-CS).

The SGW is coupled to an MGW, to at least one packet switched part(UNC-PS) and to at least one circuit switched part (UNC-CS), and isarranged i) to ensure security procedures between mobile stations andthe UMA world, ii) to forward messages relative to the control plan forboth circuit switched and packet switched core networks between mobilestations and at least one circuit switched part (UNC-CS), iii) toforward messages relative to the user plan for the circuit switched corenetwork between mobile stations and the MGW, and iv) to forward messagesrelative to the user plan for the packet switched core network betweenmobile stations and at least one packet switched part (UNC-PS).

The packet switched part (UNC-PS) is intercalated between the SGSN(s)and the SGW, and arranged for forwarding user data between this SGSN andmobile stations through the SGW, and for handling the control plan forthe packet switched core network through packet switched call messagesover TCP.

The circuit switched part (UNC-CS) is intercalated between the SGW andan MSC, and arranged for handling the control plan for the circuitswitched core network and discovery and registration procedures ofmobile stations, for forwarding packet switched call messages over TCPbetween a packet switched part and these mobile stations through theSGW, and for relaying circuit switched call messages between this MSCand the mobile stations through the SGW.

The UMA network controller according to the invention may includeadditional characteristics considered separately or combined, andnotably:

-   its packet switched part and circuit switched part may be arranged    to exchange messages through at least one TCP path, or another    transport path, such as an UDP path for instance (one means here by    “transport path” a path associated to a transport (or transmission)    protocol);-   its packet switched part may comprise a pilot station implementing    an operating and maintenance (OAM) function and chosen centralized    functions, and at least one logical service station arranged for    handling the control plan and the user plan of the GPRS traffic;    -   its circuit switched part may comprise at least one logical unit        UNC-CS arranged i) to establish a TCP connection (or another        type of transport connection such as an UDP one, for instance        (one means here by “transport connection” a connection        associated to a transport (or transmission) protocol)) with at        least one logical service station of at least one packet        switched part, ii) to handle the control plan for the circuit        switched core network and discovery and registration procedures        of the mobile stations, iii) to forward packet switched call        messages over TCP between each of the service stations and the        mobile stations through the security gateway, and to relay        circuit switched call messages between the mobile switching        center and the mobile stations through the security gateway;        -   each service station may be a functional entity supporting            one TCP connection (or another type of transport connection            such as an UDP one, for instance) per logical unit UNC-CS,            and one NSE (network service entity) per serving GPRS            serving node;        -   each logical unit UNC-CS may be arranged for selecting a TCP            path (or another type of transport path such as an UDP one,            for instance) among the ones that serves a chosen routing            area identity associated to a serving GPRS serving node. In            this case, the service station which is connected to this            chosen TCP path (or UDP path, for instance) is arranged for            selecting a network service entity among the ones that can            be selected for the chosen routing area identity;    -   each logical unit UNC-CS may be arranged, when it needs to        establish a TCP connection (or another type of transport        connection such as an UDP one, for instance), i) to require to        the pilot station of the packet switched part, the identity of        each of its active service stations and the IP address and the        TCP port (or another type of transport port such as an UDP one,        for instance (one means here by “transport port” a port        associated to a transport (or transmission) protocol)) to use in        order to establish a TCP path (or UDP path, for instance) with        each of these active service stations, then ii) to establish        effective TCP connections (or UDP connections, for instance)        with these active service station, by means of the respective        received IP addresses and TCP ports (or UDP ports, for        instance), and then iii) to send its identity, within the        established TCP connections (or UDP connections, for instance),        to the active service stations in order they send it at least        their respective identities and eventual lists of routing area        identities that they can respectively serve;        -   each active service station may be arranged to accept the            TCP connection (or UDP connection, for instance) even if all            its NSEs (network service entities) are not operational;        -   each logical unit UNC-CS may be arranged to try again            periodically to establish the TCP connection (or UDP            connection, for instance) when it fails;        -   each logical unit UNC-CS may be arranged to monitor the            availability of the TCP connections (or UDP connections, for            instance) by sending periodically a dedicated message to the            pilot and service stations of the concerned packet switched            part;    -   each logical unit UNC-CS may be arranged, when it receives a        message of an URR type from a mobile station, to choose a TCP        connection (or UDP connection, for instance) adapted to handle        messages of the URR and URLC types received from this mobile        station, then to forward the received URR message to the service        station connected to this chosen TCP connection (or UDP        connection, for instance), within a message of an UPPS type;        -   each service station may be arranged, when it receives an            UPPS message containing an URR message from a mobile            station, to allocate a NSE+BVCI (Network Service Entity+BSS            Virtual Connection Identifier) to a Cell Identifier            contained into this received UPPS message;        -   each logical unit UNC-CS may be arranged, when it receives a            message of an URR type from a mobile station and when it            manages more than one routing area identity, either to            select one of these routing area identities by means of at            least one chosen rule, or to select the routing area            identity transmitted by the mobile station, and then to            select the service station corresponding to the selected            routing area identity;    -   each logical unit UNC-CS may be arranged, when it receives a        message of an URLC type from a mobile station, to forward this        received URLC message to the concerned service station, via a        selected TCP connection (or UDP connection, for instance),        within a message of an UPPS type. In this case, the service        station may be arranged, when required and when it receives the        UPPS message comprising the URLC message, to create a context        associated to the mobile station and to forward the data        contained into the URLC message to a serving. GPRS serving node        through a network service entity associated to the routing area        identity which is associated to this serving GPRS serving node;-   its circuit switched part may be installed into a circuit switched    call server which also comprises the mobile switching center (MSC).

Other features and advantages of the invention will become apparent onexamining the detailed specifications hereafter and the appendeddrawings, wherein:

FIG. 1 schematically illustrates an example of a part of an UMA mobilenetwork comprising an UMA network controller according to the invention,

FIG. 2 schematically illustrates an example of TCP paths establishedbetween different mobile stations and logical unit UNC-CSs and betweenthese logical unit UNC-CSs and service stations (UNC-PS), and of NSEsestablished between these service stations (UNC-PS) and serving GPRSserving nodes (SGSNs),

FIG. 3 schematically illustrates the setting of TCP paths and thetransmission of the logical UNC-PS characteristics between a logicalunit UNC-CS and service stations (UNC-PS), and

FIG. 4 schematically illustrates the process of an URR-REGISTER-REQUESTmessage transmitted by a mobile station (MS) to a logical unit UNC-CS(LUi) in case where this message contains a new RAI which is not servedby the same TCP connection than an older one.

The appended drawings may not only serve to complete the invention, butalso to contribute to its definition, if need be.

In the following description it will be considered that the mobilenetwork is of the GPRS type and comprises an UMA core network.

As it is schematically illustrated in FIG. 1, an UMA mobilecommunication network comprises notably a packet switched (PS) corenetwork CN1, a circuit switched (CS) core network CN2 and at least oneUMA network controller comprising a security gateway SGW, a packetswitched part D1 and a circuit switched part D2.

The packet switched core network CN1 comprises notably at least oneserving GPRS serving node SGSN coupled to at least one packet switchedpart D1, hereafter named physical UNC-PS. The circuit switched corenetwork CN2 comprises notably a media gateway MGW and a mobile switchingcenter MSC coupled to at least one circuit switched part D2, hereafternamed physical UNC-CS.

The Security Gateway SGW is coupled to the media gateway MGW, to atleast one physical UNC-PS D1, and to at least one physical UNC-CS D2. Itis arranged to implement four main and classical functionalities.

Its first functionality consists in ensuring the security procedures(authentication, encryption and interaction with a server AAA dedicatedto authentication, authorization and accounting) between the mobilestations MS and the UMA world.

Its second functionality consists in forwarding the URR (UMA RadioResources) and URLC (UMA Radio Link Control) messages over TCPconnection between the mobile stations MS and at least one physicalUNC-CS D2. In other words, it forwards the messages relative to thecontrol plan for both circuit switched (CS) and packet switched (PS)core networks.

Its third functionality consists in forwarding the circuit switched data(such as voice over IP) between the mobile stations MS and the mediagateway MGW. In other words, it forwards the messages relative to theuser plan for the circuit switched core network CN2.

Its fourth functionality consists in forwarding the URLC messages overUDP between the mobile stations MS and at least one physical UNC-PS. Inother words, it forwards the messages relative to the user plan for thepacket switched core network CN1.

Each physical UNC-CS D2 is both connected to the mobile switching centerMSC, to the security gateway SGW, and to at least one physical UNC-PSD1. It is arranged to implement third main functionalities.

Its first functionality consists in handling the discovery procedure(redirection to the serving UNC-CS and the registration procedure of themobile stations MS in the serving UNC-CS.

Its second functionality consists in handling the control plan of thecircuit switched calls. In other words, it interfaces with the mobileswitching center MSC in order to relay the circuit switched callmessages between the mobile switching center MSC and the mobile stationsMS through the security gateway SGW.

Its third functionality consists in forwarding the URLC messages overtransport connexions between at least one physical UNC-PS D1 and themobile stations MS through the security gateway SGW. In other words, itforwards the messages relative to the control plan for the packetswitched core network CN1.

In the following description it will be considered everywhere that TCPis the transport (or transmission) protocol used between UNC-CS andUNC-PS parts of one or more UMA network controller(s) according to theinvention. So a transport connexion is a TCP connection, a transportpath is a TCP path and a transport port is a TCP port. But, theinvention is not limited to this type of transport (or transmission)protocol. It applies to other types of transport (or transmission)protocol, and notably to UDP.

Each physical UNC-CS D2 comprises one or more logical units LUi (eachdefining a logical UNC-CS).

As illustrated in FIG. 1, at least one physical UNC-CS may beco-localized with a mobile switching center MSC into a call server CSR.In a variant, at least one physical UNC-CS D2 may be co-localized with aGERAN BSC.

Each physical UNC-PS D1 is both connected to the security gateway SGW,to at least one physical UNC-CS D2 and to at least one serving GPRSserving node SGSN. It is arranged to implement two main functionalities.

Its first functionality consists in handling the control plan for thepacket switched (PS) core network, through packet switched call messagesover TCP connexions, in order to allow interworking between URLC andBSSGP (Base Station System GPRS Protocol).

Its second functionality consists in handling the user plan for thepacket switched core network CN1. In other words, it forwards the userdata between one or more serving GPRS serving node(s) SGSN and themobile stations MS through the security gateway SGW (i.e. between URLCand BSSGP).

Each physical UNC-PS D1 comprises a pilot station PSN and one or moreservice stations SSj (each defining a logical UNC-PS). According to theinvention, a physical UNC-PS D1 is physically different from a physicalUNC-CS D2, but they may be co-localized in a same site.

At least one physical UNC-PS D1 may be co-localized with a serving GPRSserving node(s) SGSN into a packet switched core network node. In avariant, at least one physical UNC-PS D1 may be part of a GPRS gateway.In another variant, at least one physical UNC-PS D1 may be co-localizedwith a GERAN PCU (PC Unit).

In order to control the use of the GPRS resources, a physical UNC-CS D2may send the expected system capacity (e.g. Routing Area (RA) and/orcell capacity), in terms of overall throughput and number of transportchannels, to a physical UNC-PS D1, at least before the first mobilestation MS registration in a cell. As an implementation option it can besignaled either in dedicated supervision messages or appended to themobile station MS registration message indicating the cell the mobilestation MS is located in. Furthermore, the physical UNC-CS D2 candynamically update the cell capacity in case of change, for example toadapt the CS/PS resource balance depending on UNC-CS criteria (time ofday, quality of the CS calls etc).

Moreover, a physical UNC-CS D2 can control the quality of service (QoS)that a physical UNC-PS D1 allocates to a mobile station MS. This can bedone either globally, i.e. per UNC-CS/UNC-PS interface, per Routing Areaor per cell, by means of supervision messages. Alternatively this can bedone per mobile station MS, for example based on the physical UNC-CS D2knowledge of UMA subscription data. Based on the allocation policyreceived, a physical UNC-PS D1 can negotiate a packet flow contextreceived from a SGSN and put in place a traffic conformance filter.

Furthermore, for a better control of the system resources, especially inoverload situation, the UNC-CS/UNC-PS control plan flows can beseparated over several TCP connections.

When there is only one UMAN (UMA Network) routing area code (UMAN RAC)whatever the location area identity (LAI—defined in the technicalspecification TS 24.008 of the 3GPP), the routing area code (RAC) isconfigured within the physical UNC-CS D2. The selection of a TCPconnection by a physical-UNC-CS D2 does not depend on the routing areaidentity (RAI) and there is one network service entity (NSE) per logicalUNC-PS SSj. It is recalled that the RAI is the concatenation of the LAIand the RAC, while the cell global identity (CGI) is the concatenationof the LAI and the cell identity (CI). Therefore, only one physicalUNC-PS can be connected to one serving GPRS serving node SGSN, otherwiseseveral SGSNs could see the same RAI. The selection of a TCP connectionby a physical UNC-CS D2 does not depend on load criteria associated toeach TCP connection (random choice of the TCP connection).

When there is more than one UMAN RAC per LAI (in other words the RAC canbe configured in the UMA database or depending on a configuration data,the RAI can be the GSM one), the RAI may be introduced as routingcriteria between a physical UNC-CS D2 and a physical UNC-PS D1. Theselection of a TCP connection by a physical UNC-CS D2 and the selectionof a NSE by a physical UNC-PS D1 depend on the RAI. Then, one servingGPRS serving node SGSN can be selected for one RAI and another servingGPRS serving node SGSN can be selected for another RAI. Therefore, aphysical UNC-PS D1 can be connected to one or more serving GPRS servingnode SGSNk. The selection of a TCP connection by a physical UNC-CS D2depends on load criteria associated to each TCP connection.

All the messages exchanged between a physical UNC-CS D2 and a physicalUNC-PS D1 use a TCP path which will be described hereafter.

Within the UMA network, the physical UNC-CS D2 and the physical UNC-PSD1 may be configured as illustrated in FIG. 2. In this FIG. 2 only twological units UNC-CS LU1 and LU2 of only one physical UNC-CS D2 and onlytwo service stations SS1 and SS2 of only one physical UNC-PS D1 areillustrated to avoid to much complexity. It is recalled that the numberof logical units UNC-CS LUi only needs to be at least equal to 1 (i>0),and the number of service stations SSj only needs to be at least equalto 1 (j>0).

A logical unit (or entity) UNC-CS LUi (here i=1 and 2) is a logicalUNC-CS that is seen as a whole physical UNC-CS D2 from the physicalUNC-PS D1 point of view.

As mentioned before, a physical UNC-PS D1 contains several servicestations SSj (here j=1 and 2) for the control plan and the, user plan ofthe GPRS traffic and one pilot station PSN for OAM (Operating AndMaintenance) and chosen centralized functions.

Each service station SSj defines a logical UNC-PS which is a functionalentity that supports one TCP connection (TCP path i) per logical unitUNC-CS LUi on the UNC-CS side, and one or more NSE (NSE k) on the SGSNside.

In FIG. 2 the first logical unit LU1 is connected to the first servicestation SS1 through a first TCP connection (TCP path 1) and to thesecond service station SS2 through a second TCP connection (TCP path 2).The first service station SS1 is connected to first SGSN1 and secondSGSN2 serving GPRS serving nodes respectively through first NSE1 andsecond NSE2 network service entities. The second service station SS2 isconnected to the first SGSN1 and second SGSN2 serving GPRS serving nodesrespectively through third NSE3 and fourth NSE4 network serviceentities. The first SGSN1 and second SGSN2 serving GPRS serving nodesare respectively associated to first RAI1 and second RAI2 routing areaidentities.

A logical unit UNC-CS LUi selects a TCP path (TCP path j) among the ones(TCP path 1 and TCP path 2) that serves a chosen RAI (RAIk) associatedto a serving GPRS serving node SGSNk and the service station SSj whichis connected to this TCP path j selects a network service entity NSEkamong the ones that can be selected for this RAI RAIk.

When there is only one UMAN routing area code, the TCP path selection bya logical unit UNC-CS LUi and the NSE selection by the service stationSSj do not depend on the RAI.

The setting of a TCP path is schematically illustrated in FIG. 3. Itconsists in two main phases.

In the first phase the IP addresses of the active service stations SSjare transmitted to the logical unit UNC-CS LUi which requiresestablishment of a TCP connection. More precisely, when a logical unitUNC-CS LUi is running, it tries to establish a specific TCP path withthe pilot station PSN of a physical UNC-PS D1. For instance the IPaddress and the TCP port of this physical UNC-PS D1 is memorized(configured) into the logical unit UNC-CS LUi (for instance the TCP portis 41000).

Then, theological unit UNC-CS LUi sends a CONFIG_INFO_REQUEST message tothe physical UNC-PS D1. When the pilot station PSN of the physicalUNC-PS D1 receives this message, it answers to the logical unit UNC-CSLUi with a CONFIG_INFO_RESULT message. This message contains threecharacteristics associated to each active service station SSj of thephysical UNC-PS D1: the identity of each active service station SSj (forinstance one IP address which is a virtual IP address) and the IPaddress and TCP port that must be used by the logical unit UNC-CS LUi toestablish one TCP connection (TCP path j) with the active servicestation SSj.

Here “active service station SSj” means hardware present andadministrative state equal to “unlock”. An active state does not dependon the configuration and state of the network service entity NSEkassociated to an active service station SSj.

For instance, if the concerned logical unit UNC-CS LUi does not receivethe CONFIG_INFO_RESULT message before an internal timer expiry, itshould resend the CONFIG_INFO_REQUEST message. If the procedure fails ntimes, it reopens the TCP connection from the beginning.

The TCP connection is kept permanently after reception of theCONFIG_INFO_RESULT message by the concerned logical unit UNC-CS LUi.

Preferably, the logical unit UNC-CS LUi monitors the availability of theTCP connection by sending periodically a KEEP-ALIVE message to the pilotstation PSN of the physical UNC-PS D1. If the logical unit UNC-CS LUidoes not receive a response to the KEEP-ALIVE message before an internaltimer expiry, it should resend this KEEP-ALIVE message. If the procedurefails n times, it reopens the TCP connection. If the TCP connectionfails, the logical unit UNC-CS LUi is responsible to reestablish it.

In the second phase the logical unit UNC-CS LUi tries to establisheffective TCP connections with the active service station SSj, usingtheir received IP addresses and TCP ports. More precisely, when thelogical unit UNC-CS LUi receives the message CONFIG_INFO_RESULT, itfirst tries to establish a TCP path with the active service stationsSSj, using each of the received IP addresses and TCP ports.

Each active service station SSj accepts the TCP connection even if allits NSEs are not operational. A NSE is operational when at least onenetwork service virtual connection (NSVC) is operational.

As long as the TCP connection establishment fails, the logical unitUNC-CS LUi tries again periodically.

When a TCP connection is established, the logical unit UNC-CS LUi sendsa SYSTEM_INFO_REQUEST message with its identity, within this TCPconnection, to the concerned active service station SSj.

Then, the concerned active service station SSj answers to theSYSTEM_INFO_REQUEST message with a SYSTEM_INFO_RESULT message containingtwo or three characteristics: its identity and the values of at leastone timer (for instance T4001 and T4003), when there is only one UMANrouting area code (RAI), and also the list of UMAN RAI that it canserve, when there is more than one UMAN routing area code per LAI.

When the logical unit UNC-CS LUi does not receive any message on a TCPconnection from an active service station SSj for a determined period,it preferably monitors the availability of the TCP connection with thisactive service stations SSj by sending periodically a KEEP-ALIVE message(Keep Alive mechanism). If one of the TCP connections fails, the logicalunit UNC-CS LUi is responsible to re-establish it.

When one service station SSj becomes active or inactive, the pilotstation PSN of its physical UNC-PS D1 can send a CONFIG_INFO_UPDATEmessage to each logical unit UNC-CS LUi to which it is connected tothrough TCP path(s). This message contains the characteristicsassociated to each of its active service station SSj (samecharacteristics as in a CONFIG_INFO_RESULT message).

When there is more than one UMAN RAI per LAI, the service station SSjcan send a SYSTEM_INFO_UPDATE message which contains the sameinformation as a SYSTEM_INFO_RESULT message, to all established TCPconnections (eventually to several logical unit UNC-CS LUi or to severalphysical UNC-CS D2) when the list of operational UMAN RAI that can beserved by one of its TCP connections is modified, or periodically inorder to send load indicators associated to the TCP connections. In thatcase, the list of operational UMAN RAI parameters is preferably notprovided.

This load indicator has a range from 0 to 100 percents. It typicallyrepresents the CPU usage in percentage of the service station SSj. Butit can also take into account several other criteria like the load stateof the TCP connection and/or the number of active contexts in theservice station SSj. These load indicators are used by the logical unitUNC-CS LUi when it receives an URR-REGISTER-REQUEST message from amobile station MS, in order to choose the TCP connection that willhandle all the URR and URLC messages received from this mobile stationMS.

When an URR-REGISTER-REQUEST message is received from a mobile stationMS, a NSE+BVCI is allocated to the Cell Identifier (LAI+RAC+Cell Id) bythe service station SSj, if not already done before.

The load indicators in the physical UNC-PS D1 are preferably computed toavoid too frequent changes.

It is important to recall that two constraints must be taken intoaccount: a cell identity (Cell-ID) and a UMAN RAI are served by one SGSNin the GPRS network, and a load must be shared correctly between theprocessing boards of the service stations of a physical UNC-PS D1. So,it is necessary to handle the service station SSj, the routing areas andthe cell. This handling can be performed as described hereafter.

In case where the service stations SSj are connected to one SGSN, eachservice station SSj supports all UMAN RAI. Therefore, when a mobilestation MS wants to be registered, it sends an URR-REGISTER-REQUESTmessage to a logical unit UNC-CS LUi which can select any TCP connectionto send an UPPS-REGISTER-REQUEST message, using a random rule or acircular rule, for instance.

When a service station SSj must send a first message related to a mobilestation MS, to a SGSN, it selects a configured network service entityNSEk.

In case where the service stations SSj are connected to several SGSN,more than one UMAN RAI can be managed by a logical unit UNC-CS LUi. So,when an URR-REGISTER-REQUEST message is received by a logical unitUNC-CS LUi from a mobile station MS, it selects a UMAN RAI by means ofrules such as the one described hereafter.

When the operator wants to manage the topology of the RAI in the UMAnetwork, he can optionally associate a UMAN RAC to a list of accesspoints in the UMA database. The UMAN location identities (UMAN CGI (UMANLAI+UMAN Cell-Id) and the UMAN RAI (UMAN LAI+UMAN RAC)) are selected bythe logical unit UNC-CS LUi if it receives them from the UMA database.

When the UMAN location identities (UMAN CGI (UMAN LAI+UMAN Cell-Id) andthe UMAN RAI (UMAN LAI+UMAN RAC)) are not received from the UMA databaseand when a configuration data is set, the location identities are theGSM location identities received from the mobile station MS.

Otherwise (location identities not received from the UMA database orlocation identities not received from the mobile station MS in case ofGPRS network not reachable by the mobile station MS and theconfiguration data is not set), a default value of UMAN RAC is allocatedby the logical unit UNC-CS LUi.

Moreover, in case where the service stations SSj are connected toseveral SGSN, the SYSTEM_INFO_RESULT and SYSTEM_INFO_UPDATE messagescontain the list of UMAN RAI (LAI+RAC) that each service station SSj cansupport. The SYSTEM_INFO_UPDATE message is sent by the service stationSSj periodically in order to send load indicators associated to it.

Therefore, when an URR-REGISTER-REQUEST message is received by a logicalunit UNC-CS LUi, it can select the most suitable TCP connection amongthe ones associated to the UMAN RAI. Then, when the service station SSjmust send a first message related to a mobile station MS, to a serviceGPRS serving node SGSNk, it selects a network service entity NSEkassociated to the RAI (RAIk).

When an URR-REGISTER-UPDATE-UPLINK message is received by a logical unitUNC-CS LUi, a new UMAN RAI is obtained, using the same rules as thosethat are used when an URR-REGISTER-REQUEST message is received.

If the new UMAN RAI is not the same as the old one, the logical unitUNC-CS LUi sends an URR-REGISTER-UPDATE-DOWNLINK message to the mobilestation MS. Within this message, the location area identification (LAI)parameter contains the new LAI and an UNC Control Channel Descriptionparameter contains the new RAC.

Then, there are two cases either the new RAI is served or not by thesame TCP connection.

If the new RAI is served by the same TCP connection, theUPPS-REGISTER-UPDATE-UPLINK message is sent to the same TCP connection.Then, when the service station SSj must send the next message related tothe mobile station MS (probably a Routing Area Update Request message),to a SGSN, it selects a NSE associated to the new RAI. It can be thesame NSE than in case of intra SGSN routing area (RA) update.

If the new RAI is not served by the same TCP connection, the logicalunit UNC-CS LUi acts as illustrated in FIG. 4.

When the new service station SSj must send a first message related tothe mobile station MS (probably a Routing Area Update Request message),to the new SGSN, it selects a NSE configured and associated to the newRAI.

The handling of the CGI can be implemented as described hereafter.

From a SGSN point of view and depending on the SGSN behaviour, eitherone cell identifier (LAI+RAC+Cell-ID) must be received from only one NSE(in other words, from the service station SSj point of view the samecell identifier must not be sent to two NSEs), or one cell identifier(LAI+RAC+Cell-ID) may be received from more than one NSE (in otherwords, from the service station SSj point of view the same cellidentifier may be sent to two NSEs).

Two different SGSN behaviors can be envisaged.

In a first SGSN behavior (one CGI must be received from only one NSE),if the whole contents of CGI were managed by the operators in the UMAdatabase, each message received from a mobile station MS by the UMAnetwork and related to the same Cell ID would be processed by the sameequipments (UNC-CS D2, UNC-PS D1 and SGSN). Such a constraint being verydifficult to manage, it is possible to structure the CGI as follows. Thestatic part of the CGI may be allocated by the operator in the UMAdatabase (it can be associated to a set of access points in the UMAdatabase), and the dynamic part of the CGI may be allocated by thelogical unit UNC-CS LUi when it receives an URR-REGISTER-REQUEST messagefrom the mobile station MS. For instance, 5 bits of the Cell ID may bereserved for the CGI dynamic part (depending on a configuration data inthe logical unit UNC-CS LUi, either the most significant bit part of theCell ID or the less significant bit part).

In a second SGSN behavior (one CGI may be received from more than oneNSE), the whole contents of CGI can be managed by the operators in theUMA database. No dynamic part is allocated by the UMA network in theCell ID.

To take into account these two SGSN behaviours, a configuration data canbe created in the logical unit UNC-CS LUi. Depending on thisconfiguration data the dynamic part of the Cell ID is either allocatedor not.

Since in the standards the SGSN cannot send more than 6 Mbits/s per CGI,it is assumed that the static part of the CGI is correctly allocated bythe operator. No control is made at the UNC-PS D1 level.

When an URR-REGISTER-REQUEST message is received by a logical unitUNC-CS LUi, it selects a TCP connection according to the criteria abovementioned, then depending on the configuration data, it either fills thedynamic part of the Cell ID using the identity of the service stationSSj associated to the chosen TCP connection or not. The resulting CGIbecomes the UMAN CGI. Then the logical unit UNC-CS LUi provides thisUMAN CGI to the mobile station MS (within an URR-REGISTER-ACCEPTmessage) and to the UNC-PS (within an UPPS-REGISTER-REQUEST message).Finally the logical unit UNC-CS LUi provides the UMAN RAC to the mobilestation MS (within an URR-REGISTER-ACCEPT message).

Then, when a service station SSj receives an UPPS-REGISTER-REQUESTmessage from the logical unit UNC-CS LUi, it associates a NSE+BVCI(Network Service Entity+BSS Virtual Connection Identifier) to the UMANCGI (if the association UMAN CGI<=>NSEI+BVCI did not exist previously)in order to prepare an exchange of messages at the Gb interface (i.einto an NSE) and it sends this UMAN CGI to the SGSN.

The handling of the URLC messages can be implemented as describedhereafter.

When a logical unit UNC-CS LUi receives an URLC message from a mobilestation MS, it forwards it to the concerned service station SSj, via theselected TCP connection, within an UPPS message. The UMAN RAC and theUMAN CGI are preferably sent to a service station SSj in all UPPSmessages.

When the service station SSj receives an URLC message within a TCPconnection, it creates a context associated to the mobile station MS (ifit has not already been created previously). All UPPS-DATA messagesreceived by a service station SSj are forwarded to a SGSN using a NSEassociated to its RAI.

The operator provisions each logical unit UNC-CS LUi in order itmanages:

-   the flag Enable_GPRS which indicates whether GPRS services for UMA    shall be offered or not,-   a configuration data that contains its identity (sent in a    SYSTEM-INFO-REQUEST message),-   a configuration data that contains one IP address of the active    pilot station PSN of the physical UNC-PS D1. This data (or value)    must be provisioned in the logical unit UNC-CS LUi when it must be    connected with at least one service station SSj, via a TCP    connection. There is only one value because a physical UNC-CS D2 is    connected to only one physical UNC-PS D1,-   a configuration data that contains the default UMAN RAC,-   a configuration data that indicates if the dynamic part of the Cell    ID is allocated or not,-   if the dynamic part of the Cell ID is allocated, a configuration    data that indicates if the most significant part or the less    significant part of the Cell ID is used for the dynamic part.

Moreover, the operator provisions each physical UNC-PS D1 in order itmanages:

-   two configuration data that contain timer information (for instance    relative to T4001 timer and T4003 timer—their default values may be    respectively 10 minutes and 30 seconds or 5 to 10 seconds),-   the NSE and NSVC,-   the characteristics related to each service station SSj:-   the identity of each service station SSj,-   the IP address and the TCP port used for TCP connection with the    service station SSj,-   the list of NSE associated to each RAI (i.e. the list of NSE that    can be selected by service station SSj for a mobile station MS    located in this RAI).

It is recalled that the association between a Cell ID and NSEi+BVCI isnot managed by the operator but is created dynamically by the UNC-PS D1.

More, the operator provisions the UMA database by associating a UMAN RACto a set of access points. It is assumed that the UMAN CGI, includingthe UMAN LAI, is already associated to a set of access points in the UMAdatabase.

To sum up, five types of messages are exchanged on the interface betweena physical UNC-CS D2 and a physical UNC-PS D1:

-   messages between a physical UNC-CS D2 and the pilot station PSN of a    physical UNC-PS D1 for TCP path setting,-   messages between a physical UNC-CS D2 and a physical UNC-PS D1 for    TCP path setting,-   messages between a physical UNC-CS D2 and a physical UNC-PS D1 for    monitoring of all TCP paths,-   messages corresponding to URR messages,-   messages corresponding to URLC messages over TCP connection.

It is recalled that the URLC messages over UDP (such as URLC UNITDATA,URLC-UFC-REQ and URLC-DFC-REQ) are exchanged between the mobile stationMS and the physical UNC-PS D1 without crossing the physical UNC-CS D2.Therefore, there is no corresponding message between a physical UNC-CSD2 and a physical UNC-PS D1.

Preferably, all messages between a physical UNC-CS D2 and a physicalUNC-PS D1, corresponding to URR or URLC messages, contain a header (forinstance encoded in “V” (fixed) format), few specific mandatoryinformation elements with fixed length (for instance also encoded in Vformat), and other specific information elements (for instance encodedin TLV format).

The URR messages may comprise a header comprising, for instance, 4octets defined exactly like the header of a corresponding URR message(Length indicator, UMA RR Protocol Discriminator, Skip indicator and URRmessage type), one octet for protocol version (only 3 lower weight bitsfor protocol version and 5 other bits are reserved), and 9 octetscontaining the IMSI (International Mobile Subscriber Identity)preferably encoded in V format.

When a logical unit UNC-CS LUi receives an URR-REGISTER-REQUEST messagesfrom a mobile station MS, and if this logical unit UNC-CS LUi acceptsthis message, it sends an UPPS-REGISTER-REQUEST to a physical UNC-PS D1.

This message is not sent to the physical UNC-PS D1 when the logical unitUNC-CS LUi answers to the mobile station MS either with URRREGISTER-REJECT or URR-REGISTER-REDIRECT.

The UMAN Cell Identity, UMAN Location Area Identification and UMANRouting Area Code must be stored in the UNC-CS context attached to themobile station MS, in order to be sent to the physical UNC-PS D1 in allthe URLC messages (UMAN Cell Identity, UMAN Location Area Identificationand UMAN Routing Area Code are mandatory in all URLC messages sent tothe physical UNC-PS D1, because it needs these information for BSSGPmessages).

If the GPRS flag is disabled in the logical unit UNC-CS LUi, it does notsend GPRS timers in the URR-REGISTER-ACCEPT message.

If the GPRS flag is enabled in the logical unit UNC-CS LUi, it shallstore the latest set of GPRS timers received from the physical UNC-PS D1and send them in the URR-REGISTER-ACCEPT all the time (i.e. even duringtemporary loss of the TCP, connexion with the physical UNC-PS D1).

An UPPS-REGISTER-REQUEST message is also sent to a new service stationSSj when an URR-REGISTER-UPDATE-UPLINK message is accepted at thelogical unit UNC-CS LUi level and if the new RAI (if any) is not servedby the same TCP connection as the old RAI.

When an URR-REGISTER-REQUEST message is received from a mobile stationMS, a NSE+BVCI is allocated to the Cell Identifier (LAI+RAC+Cell Id) bythe physical UNC-PS D1, if not already done before.

When an URR-REGISTER-UPDATE-UPLINK message is received with a new RAI bya logical unit UNC-CS LUi, it sends an UPPS-REGISTER-UPDATE-UPLINKmessage to the TCP connection used to send theURR-REGISTER-UPDATE-UPLINK message.

An URR-REGISTER-UPDATE-UPLINK message is sent by a logical unit UNC-CSLUi to a service station SSj when it receives and accepts anURR-REGISTER-UPDATE-UPLINK message from a mobile station MS, and if thenew RAI (if any) is served by the same TCP connection as the old RAI.This message is not sent to the service station SSj when the new RAI (ifany) is not served by the same TCP connection as the old RAI (in thiscase, the logical unit UNC-CS LUi selects a new TCP connection), or whenthe logical unit UNC-CS LUi answers to the mobile station MS either withan URR DEREGISTER message or an URR-REGISTER-REDIRECT message. In thesecases, the logical unit UNC-CS LUi sends an UPPS-DEREGISTER message tothe service station SSj in order to release the mobile station contextin it.

All information elements defined in the UPPS-REGISTER-UPDATE-UPLINKmessage and received in the URR-REGISTER-UPDATE-UPLINK message areforwarded unmodified. Besides, the “UMAN Cell identity”, “UMAN LocationArea Identification” and “UMAN Routing Area Code” information elementsare also provided to the physical UNC-PS D1.

When the physical UNC-PS D1 receives an UPPS-REGISTER-UPDATE-UPLINKmessage, it always accepts it (no message is returned to the logicalunit UNC-CS LUi). Then, if an UNC-PS context attached to the mobilestation MS already exists, the MS context is updated with the receivedinformation. If there is no UNC-PS context attached to the mobilestation MS, the UPPS-REGISTER-UPDATE-UPLINK message is ignored.

When a mobile station MS wants to be de-registered, it sends anURR-DEREGISTER message to the logical unit UNC-CS LUi. Upon receipt ofthis message, the logical unit UNC-CS LUi sends an UPPS-DEREGISTERmessage to the concerned physical UNC-PS D1. A mobile stationde-registration may be also initiated by the logical unit UNC-CS LUi forinstance when the TCP connection with the mobile station MS is released,or when it does not accept an URR-REGISTER-UPDATE-UPLINK, or when it hasaccepted an URR-REGISTER-UPDATE-UPLINK but the new RAI (if any) is notserved by the same TCP connection as the old RAI.

All information elements defined in the UPPS-DEREGISTER message andreceived in the URR-DEREGISTER message are forwarded unmodified in theUPPS-DEREGISTER message.

When a mobile station MS wants to get synchronization information, itsends an URR-SYNCHRONIZATION-INFORMATION message to the logical unitUNC-CS LUi. Upon receipt of this message, the logical unit UNC-CS LUisends an UPPS-SYNCHRONIZATION-INFORMATION message to the concernedphysical UNC-PS D1. When the physical UNC-PS D1 receives this message,either an UNC-PS context attached to the mobile station MS alreadyexists and the mobile station context is updated with the receivedinformation (mainly, if a transport channel exists for the mobilestation MS, it is updated with the new IP address of this mobile stationMS in order to send the URLC-UNITDATA to the correct IP address), or noUNC-PS context attached to the mobile station MS already exists (forexample, the mobile station MS is deregistered) and theUPPS-SYNCHRONIZATION-INFORMATION message is ignored.

When a service station SSj receives a BSSGP (Paging-CS-PDU) from the Gbinterface, two situations may occur. If there is a context associated tothe mobile station MS, the service station SSj sends anUPPS-PAGING-REQUEST-CS message to the concerned UNC-CS D2. If there isno context associated to the mobile station MS, the service station SSjbroadcasts this message to all the logical unit UNC-CS LUi having a TCPconnection with its physical UNC-PS D1.

Therefore, the UPPS-PAGING-REQUEST-CS message is duplicated severaltimes to the physical UNC-CS D2 (as many times as the number of servicestation SSj seen by one UNC-CS D2 (an UNC-CS D2 receiving a pagingmessage not related to the mobile station MS it serves discards it)).Since the UNC-PS D1 does not offer a mechanism to avoid that, it mustfilter the repeated CS or PS paging message.

When the UNC-CS D2 receives this UPPS-PAGING-REQUEST-CS message, twosituations may occur. If there is a context associated to the mobilestation MS, it sends an URR-PAGING-REQUEST message to the mobile stationMS. If there is no context associated to the mobile station MS, it dropsthe UPPS-Paging-Request-CS message.

It is important to notice that when an UNC-CS D2 receives anURR-PAGING-RESPONSE from a mobile station MS it does not forward it tothe concerned UNC-PS D1.

There are two types of message that are exchanged between UNC-CS D2 andUNC-PS D1 and that correspond to all URLC messages over TCP exchangedbetween a mobile station MS and a UNC-CS D2: messages from UNC-CS D2 toUNC-PS D1 and messages from UNC-PS D1 to UNC-CS D2.

These messages contain a header followed by specific informationelements.

The header may have the same structure as the one used for URR messages.So, it may contain 4 octets defined exactly like the first 4 octets ofthe header of the corresponding URLC message over TCP (Length indicator,URLC Protocol Discriminator, Skip indicator and URLC message type (whichhas only one value 0)), one octet for protocol version (only 3 lowerweight bits for protocol version and 5 other bits are reserved), and 9octets containing the IMSI preferably encoded in V format (in thedownlink direction (UNC-PS→UNC-CS) this parameter is provided only if itis available).

For messages from UNC-CS D2 to UNC-PS D1 only, the header is; preferablyalways followed by five fields encoded in V format (for instance) andone field encoded in TLV format (for instance).

The five fields encoded in V format (for instance) may be a fieldreserved for further use (for instance 2 octets), the UMAN Cell Identity(for instance 2 octets), the UMAN Location Area Identification (forinstance 5 octets), the UMAN Routing Area Code (for instance 1 octet)and the IP address of the mobile station MS (for instance 18 octets).

The field encoded in TLV format (for instance) has the same structurefor all messages between UNC-CS and UNC-PS (in both directions (uplinkand downlink)) corresponding to URLC messages over TCP. For instance, itcomprises a first octet representing the type of IEI (always equal to 0to mean “encapsulation or URLC message”) and following octetsrepresenting the whole content of the URLC message. The two first octetsof the whole content of URLC message are used for the “length indicator”which specifies the total length of the message excluding these twooctets for “Length indicator”). Thus, these octets represent also thelength of the value of the parameter “encapsulation or URLC message”.

It is important to notice that within messages from UNC-CS D2 to UNC-PSD1 and from UNC-PS D1 to UNC-CS D2, IMSI must be always provided.

The general handling of messages corresponding to the URLC messages overTCP will now be detailed.

In uplink direction, when the logical unit UNC-CS LUi receives an URLCmessage over TCP (identified by “URLC Protocol Discriminator”=2) from amobile station MS, it always sends the corresponding message to theconcerned physical UNC-PS D1. This message is encoded with firstly theIMSI, secondly the UMAN Cell Identity, UMAN Location AreaIdentification, UMAN Routing Area Code and IP address of the mobilestation MS for GPRS user data transport (filled using informationalready stored in the mobile station context), and the entire URLCmessage received from the mobile station MS (without any modification)which is put in the “Encapsulation of URLC message” parameter. Thelogical unit UNC-CS LUi sends this message to the concerned UNC-PS D1.

When the concerned UNC-PS D1 receives an “URLC” message from a logicalunit UNC-CS LUi (identified by “URLC Protocol Discriminator”=2), anUNC-PS context attached to the mobile station MS is either created orupdated with location information. Then it stores in the mobile stationcontext several information contained into the received message: theIMSI, the UMAN Cell Identity, the Routing Area Identity (which is theconcatenation of the UMAN Location Area Identification and the UMANRouting Area Code) and the TLLI (when it is received within theencapsulated URLC message).

Besides, the UNC-PS D1 preferably associates a BVCI to the UMAN CellIdentity out of the mobile station context in order to prepare exchangeof messages at the Gb interface (if not already done previously).

Finally, the URLC message received in “Encapsulation of URLC message”parameter is processed by the UNC-PS D1 according to the UMA standard.

In downlink direction, when a BSSGP UnitData message is received by anUNC-PS D1 from a SGSN, it is dropped by this UNC-PS D1 if there is nocontext associated to the concerned mobile station MS.

When a paging message is received by an UNC-PS D2 from a SGSN, thisUNC-PS D1 may broadcast it to all the UNC-CS D1 having a TCP connectionwith it, if there is no context associated to the concerned mobilestation MS.

Therefore, the paging message may be duplicated several times into anUNC-CS D2 (as many times as the number of service station SSj seen bythe UNC-CS D2 (when the UNC-CS D2 receives a paging message which is notrelated to the mobile station MS it serves, it discards it)). Since theUNC-PS D1 does not offer a mechanism to avoid that, the UNC-CS D2 mustfilter the repeated CS or PS paging message.

When, according to the UMA standard, an URLC message must be sent to amobile station MS, the UNC-PS D1 creates the corresponding message to besent to the concerned UNC-CS D2 as described hereafter. The IMSI isalways provided and the entire URLC message to be sent to the mobilestation MS is put in the “Encapsulation of URLC message” parameter ofthe message sent to the concerned UNC-CS D2.

When an UNC-CS D2 receives an UPPS message (“URLC messages over TCP”identified by “URLC Protocol Discriminator”=2) from an UNC-PS D1, ituses the IMSI received from this UNC-PS D1 to find its mobile stationcontext.

If there is no context, the UPPS message is dropped (paging messageincluded). If there is a context, the UNC-CS D2 sends the correspondingURLC message to the mobile station MS stored in this context. This URLCmessage is encoded using “Encapsulation of URLC message” parametercontent, without any modification.

The three parts (physical UNC-PS D1, physical UNC-CS D2 and SGW)defining the UMA network controller (UNC) according to the invention,may be realized with software modules, or hardware modules, or else acombination of hardware and software modules.

The invention is not limited to the embodiments of UMA networkcontroller described above, only as examples, but it encompasses allalternative embodiments which may be considered by one skilled in theart within the scope of the claims hereafter.

In the preceding description it has been described a non limitingexample of implementation of the invention in which the transport (ortransmission) protocol used between UNC-PC and UNC-PS parts of one ormore UMA network controller(s) is TCP. But, the invention is not limitedto this type of transport (or transmission) protocol. It applies toother types of transport (or transmission) protocol, and notably to UDP.

1. UMA network controller (SGW, D1, D2) for an UMA mobile communicationnetwork comprising a circuit switched core network (CN2) with at leastone mobile switching center (MSC) and a media gateway (MGW), a packetswitched core network (CN1) with at least one serving GPRS serving node(SGSN), characterized in that it comprises a security gateway (SGW), apacket switched part (D1) and a circuit switched part (D2), saidsecurity gateway (SGW) being coupled to said media gateway (MGW), to atleast one packet switched part (D1) and to at least one circuit switchedpart (D2), and arranged i) to ensure security procedures between mobilestations (MS) and an UMA world, ii) to forward messages relative to thecontrol plan for both circuit switched (CN2) and packet switched (CN1)core networks between mobile stations (MS) and at least one circuitswitched part (D2), iii) to forward messages relative to the user planfor the circuit switched core network (CN2) between mobile stations (MS)and the media gateway (MGW), and iv) to forward messages relative to theuser plan for the packet switched core network (CN1) between mobilestations (MS) and at least one packet switched part (D2), said packetswitched part (D1) being intercalated between said serving GPRS servingnode (SGSN) and said security gateway (SGW), and arranged for forwardinguser data between said serving GPRS serving node (SGSN) and mobilestations (MS) through said security gateway (SGW), and for handling thecontrol plan for the packet switched core network (CN1) through packetswitched call messages over TCP, and said circuit switched part (D2)being intercalated between said security gateway (SGW) and a mobileswitching center (MSC), and arranged for handling the control plan forthe circuit switched core network (CN2) and discovery and registrationprocedures of said mobile stations (MS), for forwarding packet switchedcall messages over TCP between a packet switched part (D1) and saidmobile stations (MS) through said security gateway (SGW), and forrelaying circuit switched call messages between said mobile switchingcenter (MSC) and said mobile stations (MS) through said security gateway(SGW).
 2. UMA network controller according to claim 1, characterized inthat a packet switched part (D1) and a circuit switched part (D2) arearranged to exchange messages through at least one transport path. 3.UMA network controller according to claim 2, characterized in that saidtransport path is chosen in a group comprising at least a TCP path andan UDP path.
 4. UMA network controller according to claim 1,characterized in that said packet switched part (D1) comprises a pilotstation (PSN) arranged for implementing operating and maintenancefunction and chosen centralized functions, and at least one logicalservice station (SSj) arranged for handling the control plan and theuser plan of the GPRS traffic.
 5. UMA network controller according toclaim 4, characterized in that said circuit switched part (D2) comprisesat least one logical unit UNC-CS (LUi) arranged for establishing atransport connection with at least one logical service station (SSj) ofat least one packet switched part (D1), for handling the control planfor said circuit switched core network (CN2) and discovery andregistration procedures of said mobile stations (MS), for forwardingpacket switched call messages over TCP between each of said servicestations (SSj) and said mobile stations (MS) through said securitygateway (SGW), and for relaying circuit switched call messages betweensaid mobile switching center (MSC) and said mobile stations (MS) throughsaid security gateway (SGW).
 6. UMA network controller according toclaim 5, characterized in that each service station (SSj) is afunctional entity supporting one transport connection per logical unitUNC-CS (LUi), and one network service entity per serving GPRS servingnode (SGSNk).
 7. UMA network controller according to claim 6,characterized in that each logical unit UNC-CS (LUi) is arranged forselecting a transport path among the ones that serves a chosen routingarea identity (RAIk) associated to a serving GPRS serving node (SGSNk),and said service station (SSj) which is connected to said chosentransport path is arranged for selecting a network service entity (NSEk)among the ones that can be selected for said chosen routing areaidentity (RAIk).
 8. UMA network controller according to claim 4,characterized in that each logical unit UNC-CS (LUi) is arranged, whenit needs to establish a transport connection, i) to require to saidpilot station (PSN) of a packet switched part (D1), the identity of eachof its active service stations (SSj) and the IP address and thetransport port to use in order to establish a transport path with eachof said active service stations (SSj), then ii) to establish effectivetransport connections with said active service station (SSj), by meansof said respective received IP addresses and transport ports, and theniii) to send its identity, within said established transportconnections, to said active service stations (SSj) in order they send itat least their respective identities and eventual lists of routing areaidentities (RAIk) that they can respectively serve.
 9. UMA networkcontroller according to claim 8, characterized in that each activeservice station (SSj) is arranged to accept said transport connectioneven if all its network service entities (NSEk) are not operational. 10.UMA network controller according to claim 8, characterized in that eachlogical unit UNC-CS (LUi) is arranged to try again periodically toestablish said transport connection when it fails.
 11. UMA networkcontroller according to claim 8, characterized in that each logical unitUNC-CS (LUi) is arranged to monitor the availability of transportconnections by sending periodically a dedicated message to the pilotstation (PSN) and the service stations (SSj) of the concerned packetswitched part (D1).
 12. UMA network controller according to claim 4,characterized in that each logical unit UNC-CS (LUi) is arranged, uponreceipt of a message of an URR type from a mobile station (MS), tochoose a transport connection adapted to handle messages of the URR andURLC types received from said mobile station (MS), then to forward saidreceived URR message to the service station (SSj) connected to saidchosen transport connection, within a message of an UPPS type.
 13. UMAnetwork controller according to claim 12, characterized in that eachservice station (SSj) is arranged, upon receipt of an UPPS messagecontaining an URR message from a mobile station (MS), to allocate aNSEi+BVCi to a Cell Identifier contained into said received UPPSmessage.
 14. UMA network controller according to claim 12, characterizedin that each logical unit UNC-CS (LUi) is arranged, upon receipt of amessage of an URR type from a mobile station (MS) and when it managesmore than one routing area identity (RAIk), either to select one ofthese routing area identities (RAIk) by means of at least one chosenrule, or to select the routing area identity (RAIk) transmitted by themobile station (MS), and then to select the service stationcorresponding to the selected routing area identity (RAIk).
 15. UMAnetwork controller according to claim 14, characterized in that eachlogical unit UNC-CS (LUi) is arranged, upon receipt of a message of anURLC type from a mobile station (MS), to forward said received URLCmessage to the concerned service station (SSj), via a selected transportconnection, within a message of an UPPS type, and said service station(SSj) is arranged, when required and upon receipt of said UPPS messagecomprising said URLC message, to create a context associated to saidmobile station (MS) and to forward the data contained into said URLCmessage to a serving GPRS serving node (SGSNk) through a network serviceentity (NSEk) associated to the routing area identity (RAIk) associatedto said serving GPRS serving node (SGSNk).
 16. UMA network controlleraccording to claim 1, characterized in that said circuit switched part(D2) is installed into a circuit switched call server (CSR) which alsocomprises said mobile switching center (MSC).